The question of whether weak, extremely low-frequency electromagnetic fields (EMFs) can cause cancer always generates heated debate (see, for example, refs 1-3). In addition to epidemiological studies, a substantial body of literature exists on EMF stimulation of cells grown in vitro (for example, refs 4, 5). Although numerous effects have been reported, many have been difficult to replicate (see refs 6, 7), and no clear biophysical mechanism has emerged. Many of the proposed mechanisms, like ion cyclotron resonance, have drawn criticism for being physically unrealistic (see ref. 9).